The most readily available source of renewable energy is the sun. Solar energy can be harnessed and converted directly into electrical energy by the use of photovoltaic collector generators or solar cells. Photovoltaic collector generators or solar cells are semiconductor devices which convert sunlight into electricity. At the heart of such devices is a semiconductor p-n junction which forms a photo diode. When the p-n junction is illuminated with light of an appropriate wavelength, an electron-hole pair is generated; the electron and the hole are pulled in opposite directions by the internal electric fields of the p-n junction. The resulting photo current can be used to drive an electrical appliance downstream such as a pocket calculator or a battery charger.
Conventional photovoltaic collector generators typically employ the use of high purity, single crystal silicon (e.g., crystal ingot) which is doped to produce either a p-type or n-type material. The doped crystal is sliced into discs or wafers and, depending upon the doping, either an electron donor or an electron acceptor is diffused into selected regions to form p-n junctions. Electrodes are then applied respectively to the diffused and nondiffused regions.
In conventional photovoltaic collector generators, the major cost factor is determined by the requirement of sawing silicon ingots into discs or wafers. Sawing is an expensive process, and results in the loss of approximately half the costly crystal ingot material as silicon dust. This technique, while resulting in the production of an acceptable photovoltaic device, is expensive and time-consuming, particularly in the cost of diamond sawing the silicon. Furthermore, the size of the collector generator is limited by the size of the wafer which is, in turn, limited by the size of the single crystal ingot. While the size may be increased using cast silicon sheet, the costs are commensurately increased by the use of such techniques.